A cylinder assembly is a typical fluid-operated device. Generally, the cylinder assembly includes a cylinder having first and second ports and slideably housing a piston for movement between extended and retracted positions to move a load. To control movement of the piston and the load, a valve assembly is provided in fluid communication with a source of fluid pressure and with one or both of the ports of the cylinder assembly. The valve assembly may include a locking valve which operates to control movement of the piston upon interruption of the source of fluid pressure.
In one construction, a single locking valve is in fluid communication with one port and controls movement of the piston upon interruption of a source of fluid pressure to only that port. In another construction, a locking valve is fluidly connected to each port, and each locking valve operates independently to control movement of the piston upon interruption of the source of fluid pressure supplied to the corresponding port. In either construction, the locking valve operates to maintain the piston and the load supported by the cylinder assembly in a relatively stationary position after the interruption of the source of fluid pressure.
To release the fluid pressure from the system after operation of a locking valve, a release valve may be incorporated into the valve assembly. An example of such a release valve is disclosed in U.S. Pat. No. 4,838,306.